Geotechnical Design and Rock Support Evaluation of Dimapur–Kohima Railway Tunnel, Nagaland, India

Abstract

This study evaluates the rock support requirements for a specific tunnel design, aligning with guidelines from the Indian Railways Schedule of Dimensions for 1676 mm Broad Gauge (BG), Revised (2004), and Addendum and Corrigendum Slip (ACS) No. 26. By examining geological, geotechnical, and geo-engineering parameters along the tunnel alignment— including rock mass characteristics and in situ stress conditions—the study aims to identify optimal design and support systems. Using RocLab software, key rock mass properties like deformation modulus and shear strength were evaluated, while RS2 (Finite Element Method software) assessed primary tunnel support needs. For full-face excavation and tunnel cross sections without invert, the recommended support classes III and IV require bolts of 3–3.5 m in length and 10–15 cm shotcrete. For cross sections with invert, classes IV, V, and VI support systems are advised. The maximum observed deformation for Class VI tunnels ranged from 80–150 mm, with a yielding radius of approximately 8 m, indicating poor rock quality in this section. To mitigate deformation risks, a high-strength support system with yielding capabilities is suggested, along with pipe roofing. However, further evaluation through 3D simulations is recommended to assess the pipe roof’s effects on stress and deformation. Finally, Class VII supports are proposed for their robust design, especially in areas with shallow overburden and low-stress environments, capable of managing substantial loads. This real-time study offers valuable insights for academicians and consultants focused on tunnel support assessment and related geotechnical applications.